Stack Effect

This is a naturally-occurring phenomenon of vertical structures where the building heats air which then rises and escapes through the top of the building. This creates a vacuum which draws new air in the bottom. Thus, air continues to come in the bottom of the building, and circulate out the top.

This is very problematic in the case of high-rise fires. As the fire heats the air, the air escapes upward, drawing new air in below the fire to feed it, and creating an artificial wind which pushes the fire up the building.

Occasionally, in very hot climates, you get a “reverse stack effect” where the air conditioning in the building cools the outside air, lowering its temperature, and causing it to settle and come out the bottom.

This phenomenon is the basis for things like solar chimneys and solar updraft towers.

Why I Looked It Up

This came up in a book about skyscraper construction. It’s a huge design consideration, apparently.

Also, it immediately got me thinking about shower curtains. I had always known that shower curtains tend to blow inwards at the bottom when taking a shower. I thought that this is because the hot water heated the air, which essentially caused (what I now know to be) a stack effect inside the shower.

However, the Wikipedia page on Shower-Curtain Effect states that this likely isn’t so, since apparently it still happens when cold water is used (I don’t take many cold showers). The page says the phenomenon is not totally understood, but the Bernoulli Principle is the most accepted explanation. It theorizes that the water coming out of the shower head accelerates the air it travels through, which lowers its pressure.

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